Just as a thought experiment, I tried
http://www.bikecalculator.com/
for a 70 kg (154 lb) rider on a 27 kg (60 lb) bike, this will give you a sense of how hard this would be:
Power (motor plus legs) --> Speed kph / Speed mph
200W --> 31 kph / 19.3 mph
300W --> 36.2 / 22.5 (100W adds 3.2 mph)
400W --> 40.3 / 25.0 (+2.5 mph)
500W --> 43.8 / 27.2 (+2.2 mph)
600W --> 46.8 / 29.1 (+1.9 mph)
700W --> 49.5 / 30.7 (+1.6 mph)
800W --> 52.0 / 32.3 (+1.6 mph)
900W --> 54.2 / 33.7 (+1.4 mph)
1,000W --> 56.3 / 35.0 (+1.3 mph)
*****
5,000W --> 98.2 / 61.0 mph
*****
10,000W --> 124.2 / 77.1 mph
*****
150cc vespa = 8650 W (11.6 hp) (less at the rear wheel)
Honda CBR300 = 20,730W (27.8 hp) (measured at the rear wheel)